piclist 2002\10\23\175441a >
Thread: Winding inductor for 2 trans. LED blinker
face BY : Russell McMahon email (remove spam text)

> *>Can a simple oscillator circuit (555, coupled inverters, etc) be induced
> *>to use an inductor instead of a capacitor as the energy storage element?
> Coupled gates oscillators will work with an inductor. The inductor should
> shunt a gate afair (instead of a feedback resistor).

Interestingly (perhaps) I've just used a gate shunting inductor in a crystal
oscillator to "solve" an otherwise intractable problem. The entire presently
available production (latest date code) of a particular model of non-PIC
microprocessor has startup problems in certain circumstances. Everything
else I tried failed to adequately improve the results. Adding a 22 uH
inductor across the crystal made a very substantial difference. While an
inductor in this location notionally "cancels" an equivalent amount of
capacitive reactance in the crystal at the operating frequency, in practice
the results are far more extensive than might be expected. Changing the two
capacitors from either leg of the crystal to ground in various ways produces
interesting results. It is possible (not recommended!) to obtain oscillation
output outside Vdd and ground (due to LC tank) and to have the oscillator
input waveform of higher amplitude than the output.

The inductor used is one of the small barbell cored ones such as Roman is
using in his Black Converter and has a dc resistance of about 1 ohm. Smaller
and larger values work but 22 uH seems optimum for my requirement. The
inductive reactance is only about 1,100 ohms at crystal resonance.

               Russell McMahon

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